A tungsten electrode material has conventionally been disclosed in U.S. Pat. No. 6,051,165 (PTL 1), Japanese National Patent Publication No. 2005-519435 (PTL 2), Japanese Patent Laying-Open No. 2005-285676 (PTL 3), Japanese Patent Laying-Open No. 2006-286236 (PTL 4), and Japanese Patent No. 4486163 (PTL 5). A work function of tungsten is disclosed in Japanese Patent Laying-Open No. 2010-161061 (PTL 6).